The present invention relates to a drive system of an EL display panel and, more particularly, to a memory erase drive and memory read-out drive in an EL display panel which shows memory characteristics.
A thin-film electroluminescent element of a three-layer construction is well known in the art, which comprises a semiconductor electroluminescent thin film made of, for example, a ZnS layer doped with Mn (ZnS:Mn) and a ZnSe layer doped with Mn(ZnSe:Mn) sandwiched between a pair of dielectric thin films made of Y.sub.2 O.sub.3, Si.sub.3 N.sub.4 or TiO.sub.2. The above-mentioned thin-film electroluminescent element exhibits electroluminescence of high brightness upon receiving A.C. voltage signal of several kilohertz. And, the above-mentioned thin-film electroluminescent element shows the long life operation.
By properly controlling the amount of Mn doped within the electroluminescent layer and the fabrication conditions, the above constructed thin-film EL element exhibits the hysteresis properties within light intensity versus applied voltage characteristics as disclosed in Y. KANATANI et al, U.S. Pat. No. 3,967,112, "PHOTO-IMAGE MEMORY PANEL AND ACTIVATING METHOD THEREOF" on June 29, 1976.
Generally, when light energy, an electric field or heat energy is applied to the thin-film EL element having the hysteresis characteristics under a condition where the applied voltage is increased, the thin-film EL element is excited to exhibit light emission corresponding to the applied energy. The thus obtained light emission is held or memoried even after the application of the light energy, the electric field or the heat energy is terminated. By effectively utilizing the above-mentioned memory phenomenon, the thin-film EL element can be applied to various technical fields.
Accordingly, an object of the present invention is to provide a novel drive system for a thin-film EL element having hysteresis characteristics.
Another object of the present invention is to provide a drive system for erasing memoried information in a thin-film EL element having hysteresis characteristics.
Still another object of the present invention is to provide a drive system for reading-out memoried information in a thin-film EL element having hysteresis characteristics.
Yet another object of the present invention is to combine a sustaining voltage signal with an electron beam erase signal in a thin-film EL display panel which shows hysteresis characteristics.
A further object of the present invention is to combine a sustaining voltage signal with an electron beam read-out signal in a thin-film EL display panel which shows hysteresis characteristics.
Other objects and further scope of applicability of the present invention will become apparent from the detailed description given hereinafter. It should be understood, however, that the detailed description and specific examples, while indicating preferred embodiments of the invention, are given by way of illustration only, since various changes and modifications within the spirit and scope of the invention will become apparent to those skilled in the art from this detailed description.
To achieve the above objects, pursuant to an embodiment of the present invention, a thin-film EL display panel is provided which comprises a thin-film EL layer made of, for example, a ZnS:Mn thin film sandwiched between a pair of dielectric layers made of Y.sub.2 O.sub.3, Si.sub.3 N.sub.4 or TiO.sub.2. A front transparent electrode made of SnO.sub.2 or In.sub.2 O.sub.3 is formed on one of the dielectric layers, and a rear metal electrode made of, for example, aluminum is formed on the other dielectric layer. The thus formed thin-film EL element is supported by a glass substrate in such a manner that the front transparent electrode confronts the glass substrate.
The above constructed thin-film EL display panel is disposed at a display surface of a cathode-ray tube in such a manner that the glass substrate is exposed to the outside. An electron beam generator is disposed at an end of the cathode-ray tube for applying an electron beam to the thin-film EL display panel through the rear metal electrode.
An alternating sustaining voltage signal is applied to the thin-film EL element through the use of the front and rear electrodes in order to maintain the information displayed on the thin-film EL display panel. An electron beam is applied from the electron beam generator to a desired position on the thin-film EL display panel at a time when the sustaining voltage signal bears the zero level, thereby erasing the memoried information.
The memoried display information is electrically read out by detecting a polarization relaxation current which flows through a memoried display position when an electron beam is applied thereto.